Explain Energy (is it physical)?

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Discussion Overview

The discussion centers around the nature of energy, specifically whether it can be considered a physical entity. Participants explore various definitions and conceptualizations of energy, touching on its abstract qualities and its role in physics.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that energy is a property of movement and potential movement, likening it to kinetic energy, speed, or momentum.
  • Others argue that energy is defined as the ability of one system to perform work on another, with some expressing dissatisfaction with this definition due to its abstract nature.
  • A participant mentions the conservation of energy as a fundamental principle, emphasizing its mathematical aspect rather than a concrete mechanism.
  • There is a suggestion that energy might be viewed as a "bookkeeping" device, used to account for changes in systems rather than a tangible object.
  • Some participants question the meaning of "physical" in the context of energy, suggesting that it may not refer to a material object but rather to a measurable attribute of systems.
  • One participant notes that while energy can be associated with physical phenomena, such as photons, it is not a physical object in itself.
  • Another participant highlights the difficulty in providing a straightforward definition of energy, suggesting that it is often explained through intuitive examples rather than a comprehensive description.

Areas of Agreement / Disagreement

Participants express a range of views on the nature of energy, with no consensus reached on whether it should be considered physical or merely an abstract concept. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants note limitations in definitions and the abstract nature of energy, as well as the dependence on context when discussing its physicality. The conversation reflects a variety of interpretations and assumptions regarding the concept of energy.

  • #61
OmCheeto said:
Voko's answer looked like the following: Click to see

Nah, you dreamed incorrectly :)

The kinetic and potential energies are not deduced from a Hamiltonian or a Lagrangian. They are required to formulate those things to begin with, so they are "given" pretty much like forces are "given" in the Newtonian formalism.

And writing equations with energies is not really more complex than with forces, to put it mildly. The success of the Lagrangian mechanics is a solid confirmation.
 
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  • #62
voko said:
A scale can have the pivot at the same level or even lower than the points where the pans are attached, and it can have a rigidly attached counter-weight below the pivot, so the entire rotating assembly is T-shaped. This will have stable equilibria within a range of mass deltas.

Fair enough, I hadn't thought about using a counterweight to provide a moment to counteract the instability.

But with my mindset of working in aerospace, a counterweight is just an extra part in the device and extra mass, and those are two good reasons for not having one if you can make a design that works without it. :smile:

(Of course a torsion spring would be lighter than a counterweight, and provide the same functionality)
 
  • #63
AlephZero said:
But with my mindset of working in aerospace, a counterweight is just an extra part in the device and extra mass, and those are two good reasons for not having one if you can make a design that works without it. :smile:

A have seen a few "chemist" style scales, and they had a tall stand, a dial at the bottom, and the pointing needle (more like a spear) all the way from the fulcrum to the dial. I think it doubled as a counterweight. I cannot say with certainty, however, that the fulcrum was "low" in them, so they could have been a combination design.
 
  • #64
But interesting as this digression on scales may be, it doesn't change the point I was trying to make in my first post, which is that all these designs are just as easy to understand using "forces and moments" as using energy. Either way, you need to understand the kinematics of the machine to make a mathematical model of it.
 
  • #65
AlephZero said:
But interesting as this digression on scales may be, it doesn't change the point I was trying to make in my first post, which is that all these designs are just as easy to understand using "forces and moments" as using energy. Either way, you need to understand the kinematics of the machine to make a mathematical model of it.

I do not disagree. My idea that balance scales can be tricky was a result of quite a few discussions with somebody having a hard time with some particular variety of balance scales.
 
  • #66
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